Typically, high Mooney EAODM polymers produced by solution or slurry polymerization processes are sold as bales and with oil already imbibed to allow for easier processing and handling. Generally, if these polymers are to be sold in pellet or powder form they must be coated with a partitioning agent to prevent agglomeration of the particles into a large mass or bale.
EP 0775718A2 teaches the use of gas phase EAODM in TPV's and thermoplastic polyolefins. EAODM is produced by a gas phase process in powder or pellet form. However, these EAODM polymers, in powder or particle form, tend to absorb oil relatively slowly.
TPV's are generally produced by dynamic vulcanization of elastomeric polymers such as EAODM polymers in a thermoplastic matrix polymer. Generally, a thermoplastic polymer and elastomer should be intimately melt mixed prior to vulcanization as discussed in C. P. Rader and S. Abdou-Sabet, “Two-phase elastomer alloys,” in S. K. De and A. K. Bhowmick, eds., Thermoplastic Elastomers from Rubber-Plastic Blends, Ellis Horwood, New York, 1990, pp 159-197 and U.S. Pat. No. 4,311,628; Bhowmick A. K. and Inoue T., Journal of Applied Polymer Science, Vol. 49 (1993) page 1893. During dynamic vulcanization, the elastomer is converted to a crosslinked material dispersed as small particles in a continuous thermoplastic matrix. The result is a useful composition or TPV having the melt processability of thermoplastics combined with the rubber-like properties of crosslinked elastomers, including elastic recovery, heat resistance; compression set resistance, and softness.
According to Coran A. Y. and Patel R., Rubber and Chemical Technology, Vol. 53, (1980), p. 141 it is preferable to produce a melt dispersion containing the smallest polymer particle size for the rubber phase as possible before crosslinking which yields a TPV with superior physical properties such as tensile strength and elongation.
U.S. Pat. No. 4,130,535 teaches that a curative is preferably added to a mixture of elastomer, thermoplastic, and filler. The reason for the preference of the first method is not stated, but one possible theory is that the delayed addition of curative allows a finer particle morphology to be developed prior to the onset of crosslinking, which “locks in” the particle size/shape. Thus, by mixing the polymers and optionally added fillers, plasticizers, and other additives first, and only adding the curative after these are well melt-mixed, a small particle size and improved physical properties might be obtained.
It would be beneficial if an improved and easier method could be found for producing finely dispersed elastomer or EAODM particles in a thermoplastic polymer melt mixture, resulting in TPVs with improved physical properties.